Trump’s Hormuz blockade: Another nail in the coffin of the rules-based order

In October 1962, US President John F. Kennedy’s advisers had a problem. The United States intended to stop Soviet ships carrying missiles to Cuba, but the word “blockade” could not be used. A blockade, under the law of naval warfare, is an act of war. Robert Kennedy, who had been reading Barbara Tuchman’s The Guns of August during the crisis, understood what that meant. The administration settled on “quarantine”, a word with no precise legal meaning and therefore no automatic legal consequences. The Soviet ships turned back. The quarantine worked partly because everyone understood it was a blockade, and also because Kennedy had secured Organisation of American States backing before announcing it.

Sixty-four years later, Donald Trump has less patience for such distinctions.

On Sunday, April 13, after peace talks brokered by Pakistan collapsed following twenty-one hours of negotiations, Trump announced that the US Navy would blockade the Strait of Hormuz. “BLOWN TO HELL,” he wrote on Truth Social, referring to anyone who fired at American vessels or peaceful shipping. The blockade went into effect at 10 am Eastern time on Monday, April 14.

More from Opinion

The legal situation is genuinely complicated, and worth unpacking shorn of political noise. Iran, Israel and the United States are all belligerents in an armed conflict that commenced on February 28. Under the San Remo Manual on International Law Applicable to Armed Conflicts at Sea, the codified framework for naval warfare, belligerents may impose blockades. The right of visit and search applies. Warships can stop and inspect private vessels in non-neutral waters. The United States can legally blockade Iranian ports. That much is settled.

But “legal” here covers a great deal of complexity. The United States is not a party to the United Nations Convention on the Law of the Sea, though it is bound by customary international law on freedom of navigation. Jason Chuah, professor of maritime law at City St George’s, University of London, has argued that what Washington is doing is not a classic blockade but “sanctions with warships doing the bidding of President Trump,” a pattern of stopping, boarding and seizing vessels linked to Iran.

The San Remo Manual sets a high lawfulness bar. A blockade must be declared, effective and applied even-handedly to neutral ships. A country cannot enact a blockade with the goal of starving a civilian population. The US Department of Defense’s own law of war manual states that neutral vessels carrying relief supplies should be allowed to pass.

The CENTCOM notice to mariners, issued as the blockade went into effect, says the ways enforcement measures “will be applied in practice... are in development.” Sixteen US warships are in place; none are currently inside the Persian Gulf itself. The enforcement geography covers the entire Iranian coastline, extending eastward through the Gulf of Oman into parts of the Arabian Sea. Any vessel entering or departing without authorisation is, in CENTCOM’s phrasing, “subject to interception, diversion and capture.”

There are several enforcement challenges. Iran’s coastline across the Persian Gulf and Gulf of Oman stretches 1,340 miles. In peacetime, roughly 150 vessels transit Hormuz daily. In March, a little over 150 passed through the entire month, according to S&P Global Market Intelligence. Tanker Trackers, a shipping intelligence firm, flagged the problem of AIS spoofing on day one, Iran-linked tankers regularly make false port calls in Saudi Arabia and Iraq, changing identification data to evade detection. Ship-tracking data showed two vessels, the Rich Starry and the Ostria, turning back on the blockade’s first day.

Iran has spent considerable effort making itself hard to strangle quickly. Ernest Censier of Vortexa, a commodity data firm, estimates Iran may be forced to curb production within ten to twenty days of a fully effective blockade, given current storage levels. The critical qualifier is “fully effective.” Iran exported 1.84 million barrels per day in March and 2.15 million in February, roughly 26 percent above 2025 levels. As of late March, Kpler estimates 154 to 160 million barrels of Iranian crude were floating outside the Persian Gulf, enough to supply China’s independent teapot refiners (who absorb over 90 percent of Iranian exports) until approximately mid-July.

The Foundation for Defense of Democracies estimates the blockade will cost Iran around $435 million per day, including $276 million in lost exports, based on 1.5 million barrels per day at $87 a barrel, assuming over 90 per cent transits through Kharg Island inside the Gulf. How much oil Iran can reroute through its Jask terminal on the Gulf of Oman, which sits outside the strait, remains a significant unknown.

The counter-escalation risk runs in the opposite direction entirely. Saudi Arabia, which has diverted crude exports from its Ras Tanura terminal in the Persian Gulf to the Red Sea port of Yanbu via overland pipeline, now risks losing its second route as well. Iran is pressing the Houthi movement in Yemen to close the Bab al-Mandeb, the passage between Yemen and the Horn of Africa that connects the Red Sea to the Indian Ocean.

Before the Gaza conflict, 9.3 million barrels per day moved through Bab al-Mandeb. Houthi attacks during that period halved the figure. Ali Akbar Velayati, foreign policy adviser to Iran’s supreme leader, said in early April that Iran views Bab al-Mandeb “just as it looks at Hormuz.” The USS George H.W. Bush, the third American carrier deploying to the region, is routing around the Horn of Africa rather than through the Red Sea, confirming that the threat is taken seriously even if it is not publicly acknowledged as such.

The consequences of sustained closure extend well beyond oil. Around 30 per cent of the world’s fertilizer transits Hormuz. American drivers are currently paying $4.12 per gallon on average, up from $2.98 before the war began. Brent crude is above $100 a barrel. The Financial Stability Board’s chair, Andrew Bailey, who also governs the Bank of England, has warned of a “triple whammy” of sovereign bond, asset valuation and private credit risks crystallising simultaneously. The IMF, IEA and World Bank met in Washington on Monday to describe the war’s impact as “substantial, global, and highly asymmetric, disproportionately affecting energy importers, in particular low-income countries.”

There is a structural irony in this whole episode. The United States has historically been the most forceful advocate for freedom of navigation through international straits. It invoked UNCLOS Article 38’s guarantee of transit passage repeatedly against Chinese claims in the South China Sea, even though it has never ratified the convention. The principle that international straits must remain open to all has been a cornerstone of American foreign policy for decades. Rightly the blockade is “another nail in the coffin for any pretence that there is such a thing as a rules-based order or international law.”

Kennedy called it a quarantine because he understood that words carry legal weight, and that escalation has its own momentum. His quarantine lasted 13 days. The US wants this to be a short operation. But it doesn’t seem to be the case. The strait will open when it opens. That much, at least, is not in development.

(Aditya Sinha [X: @adityasinha004] writes on macroeconomics and geopolitics. Views expressed in the above piece are personal and solely those of the author. They do not necessarily reflect Firstpost’s views.)